Fiber-reinforced composite materials composed of various fibers and a matrix resin are widely used in automobiles, railroad vehicles, aircrafts, ships, sporting goods, and other general industrial applications for their excellent dynamical properties.
The range of applications of fiber-reinforced composite materials have recently been expanding more and more as their performance in actual use is accumulated.
As examples of such fiber-reinforced composite materials, there have been proposed those utilizing compounds having a benzoxazine ring, for example, in Patent Publications 1 and 2. These compounds having a benzoxazine ring are excellent in resistance to moisture and heat, but inferior in toughness. Attempts have been made to compensate for this defect by admixing epoxy resin or various fine resin particles.
On the other hand, there has been a demand for further weight saving of fiber-reinforced composite materials which are applied to the main structures in automobiles, railroad vehicles, aircrafts, ships, sporting goods, and other general industrial applications, by achieving, among the dynamical properties required for these applications, particularly the compression-after-impact strength (abbreviated as CAI hereinbelow), the interlaminar shear strength (abbreviated as ILSS hereinbelow) at high temperature and humidity, and the interlaminar fracture toughness, all at the same time at high levels. In addition, for maintaining high-temperature characteristics, the glass transition temperature of the resin material used therein needs to be maintained at a high level. However, it cannot be said that the examples specifically disclosed in the Patent Publications mentioned above are capable of necessarily achieving these properties concurrently at high levels.
As a technology for improving the dynamical properties, Patent Publication 3, for example, discloses to add polyamide 12 fine particles to a thermosetting resin, such as epoxy resin, for improving CAI.
Fiber-reinforced composite materials utilizing such technology are capable of maintaining the CAI at a certain high level, but are yet to achieve high CAI and ILSS at high temperature and humidity at the same time.
Patent Publication 4 discloses, as a carbon fiber composite material satisfying both CAI and ILSS concurrently at high levels, a composite material having a laminated structure of resin layers containing particular polyamide fine particles and carbon-fiber-containing layers laminated alternatively.
However, this Publication does not specifically disclose a composite material of a laminated structure containing a compound having a benzoxazine ring. Development of a material is demanded which is capable of exhibiting excellent characteristics of a compound having a benzoxazine ring, and has still more excellent CAI.
Patent Publication 1: JP-2007-16121-A
Patent Publication 2: JP-2010-13636-A
Patent Publication 3: JP-2009-286895-A
Patent Publication 4: JP-2009-221460-A